Kelsier and his brother Marsh were the sons of a Noble father and a Skaa mother. When Kelsier's father discovered the truth of their parentage he had their mother executed and attempted to do the same to the brothers, who fled. This created a sense of resentment of the nobility in both children, which resulted in Marsh becoming the leader of the Skaa Rebellion and Kelsier became a crewleader for a gang of Misting thieves, stealing from the noble families. He fell in love with a Tineye crewmember named Mare, whom he later married. Marsh, who was also in love with Mare, came to resent Kelsier for winning her love and for constantly outshadowing him.

Despite having amassed enough wealth to live comfortably, Kelsier continued planning more heists, looking for bigger challenges in each. In their last heist, Kelsier's crew planned to steal the Lord Ruler's atium cache from Kredik Shaw. However, Mare's use of allomancy is sensed by the Steel Inquisitors, as they could pierce the copperclouds, and Kelsier and Mare are captured by the Lord Ruler. The Lord Ruler thanks Mare, causing Kelsier to conclude that Mare betrayed him.

Kelsier was sent to the the Pits of Hathsin, to mine Atium for the Lord Ruler. Mare joined him there a few months later. He still loved her, but couldn't trust her. Sixteen months later, when Kelsier was unable to get his weekly atium geode, Mare gave Kelsier hers, claiming that she had found two that week. Kelsier discovered that Mare had given him her only geode, and was forced to watch Mare being beaten to death by the guards. Kelsier protested, earning himself a violent beating. This caused him to Snap, awakening his Mistborn powers. He killed the guards and escaped the Pits of Hathsin, killing all the nobility he encountered in the vicinity of the Pits.

Kelsier began to travel and in the following years learned the art of Allomancy from an old Skaa Mistborn named Gemmel. He also searched far and wide for possible ways to defeat the Lord Ruler, and managed to find a bar of the fabled Eleventh Metal. Despite his suspicion that Mare betrayed him, he decides to fulfill Mare's dream of overthrowing the Final Empire. When Kelsier is offered a deal by Yeden to overthrow the Lord Ruler, he quickly accepts.

Travelling back to Luthadel, he begins to assemble a thieving crew to put his plan into motion. His best friend, Dockson, helps him follow up on Marsh's reports of a Skaa Mistborn, finding Vin. He also convinces Breeze, Ham and Clubs to join the conspiracy by offering a share of the Lord Ruler's stash of valuable Atium as loot. Vin joins in exchange for Kelsier's training. Kelsier's estranged brother Marsh also joins, hoping to realize his own dream of a successful Skaa Rebellion despite his disapproval of Kelsier's methods.

Kelsier's role takes advantage of his Mistborn training, allowing him to assassinate Nobles in order to destablize the Great Houses and use his reputation as the Survivor of Hathsin to inspire the newly-trained Skaa soldiers. However, he slowly comes to realize that the Skaa people are too downtrodden for the Rebellion to succeed and begins to change his plans. After the destruction of Yeden's army in a disastrous raid, he rallies the troops.

Kelsier changes plans, destroying the Atium-producing crystals in the Pits of Hathsin and halting the production of Atium in the near-future. As the Lord Ruler begins randomly executing Skaa in an attempt to quell the populace, Kelsier attacks and frees the prisoners, killing a Steel Inquisitor in the process. However, he is himself confronted by and killed by the Lord Ruler himself.

Kelsier has the KandraOreSeur ingest his remains, masquerading as a resurrected holy figure. OreSeur incites the Skaa to rebel, beginning the revolution and the overthrow of the Final Empire. After his apprentice Vin kills the Lord Ruler, OreSeur lays Kelsier's bones to rest. Kelsier's martyrdom and seeming resurrection spawns a new religion, the Church of the Survivor, which venerates Kelsier's teachings.

Kelsier is brave, charismatic and optimistic. A natural leader, Kelsier used his charismatic personality to draw skilled and loyal Mistings to his own crew and eventually to lead an army to destroy the Final Empire. Optimistic to a fault, Kelsier claims that he smiles solely because laughter is the only thing that the Lord Ruler cannot take from them. His cheerful exterior hides his doubts over Mare's loyalty, whom he continues to believe had betrayed him until Vin demonstrates that it is possible to pierce copperclouds.

Kelsier is also highly impulsive, on one occasion attempting to attack an entire army single-handedly.

He is shown to be ruthless and prejudiced, killing nobility and the Skaa who serve them with absolutely no qualms. He overcomes this character flaw eventually, when Vin convinces him that there are good people among the nobility.

Kelsier is a fully trained Mistborn, despite his half-Noble half-Skaa ancestry. Although he has only come into his powers three years before the beginning of Mistborn: The Final Empire, Kelsier repeatedly demonstrates a level of power and finesse greater than that of most other Mistborn. In addition, Kelsier is a competent warrior, defeating multiple hazekillers and Mistings while outnumbered and disarmed.

Although Vin assumes him to have only trained partially using each metal, Kelsier is extremely skilled at Steelpushing and Ironpulling, a skill he demonstrates when he defeats and kills the Steel Inquisitor Bendal.